fix(engine): leave scribe marks out of layout bounds and salvage

The job runner already checked sheet bounds on material contours only,
but the benchmark validator and salvage scoring used Part.BoundingBox,
which includes scribe/etch moves. A PEP bend tick that ends a hair past
the part's edge passed the runner yet failed the benchmark when placed
flush to the sheet edge, and it could shrink the credited offcut. Marks
only mark the surface, so bounds and salvage now use material only.

Benchmark before/after (all five built-in engines, local fixtures,
salvage 0.5): no job changed validity or cost. Regression tests pin the
new rule: a protruding tick flush to the sheet edge is valid in all four
quadrants, and a tick past the parts envelope no longer shrinks salvage
(targeted fixture cost 130 -> 120).

Co-Authored-By: Codex <noreply@openai.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

OpenNest.Engine/Jobs/NestLayoutCheck.cs

@@ -225,7 +225,7 @@ public static class NestLayoutCheck
 
         foreach (var part in parts)
         {
-            var bb = part.BoundingBox;
+            var bb = MaterialBounds(part);
 
             var outLeft = bb.Left < workArea.X - Tolerance.Epsilon;
             var outBottom = bb.Bottom < workArea.Y - Tolerance.Epsilon;
@@ -339,6 +339,13 @@ public static class NestLayoutCheck
         }
     }
 
+    /// <summary>Analytic world-space material bounds; surface marks never bound material.</summary>
+    internal static Box MaterialBounds(Part part) =>
+        ConvertProgram.ToGeometry(part.Program)
+            .Where(e => SpecialLayers.IsMaterial(e.Layer))
+            .GetBoundingBox()
+            .Translate(part.Location);
+
     private static bool BoxesTouch(Box a, Box b) =>
         a.Left <= b.Right + Tolerance.Epsilon
         && b.Left <= a.Right + Tolerance.Epsilon